A7;/../r.s i\ rill-: hell svstv.m 25 



III adiliiioii the m.i\iniiini ii->i>t,iiicr of tlu- Iriiiik i> i:{(Ht (ihm>. llu' 

 linr ri-liiy must lluTi'lori- hi- ailjiisU'd lo oixT.ilt.' "wv lliis rusistancc- 

 .111(1 in si-rii's with tlic sti'ppinjj n-lay wiu-ii llu- lialltiy potential is 

 a inininniin of 44 \-olts. It must also he ailjusteii lo release (juickly 

 i'Uoiij;h to insure the p<)siti\e selection of a particular terminal when 

 the battery potential is a maximum of 52 \()lts and both the trunk 

 iMpacit\' ami trunk leakage are maxinuim. These are \cry se\'ere 

 reciuirements to be met by a rela\- which is produced commercially in 

 lar.ye (juantities at a small cost; and more sc\ere conditions such as 

 would result, for example, from increasing the length of the trunk 

 could not be imposed on this particular rela\' unless the iron struc- 

 ture were maile frcm s )me new material ha\ing more faxorahle 

 magnetic constants. 



The requirements for the stepping relay, howe\er, are more se\ere 

 than those for the line relay, for the stepping relay must continually 

 operate and release as the commutator brush alternately grounds 

 and frees the trunk in the distant office. Also the insulation resistance 

 and capacity of the trunk exert a somewhat different influence on the 

 functioning of the stepping relay than on the functioning of the line 

 relay. The trunk leakage current resulting from low insulation 

 resistance interferes with the operation of the stepping rela\-, instead 

 of its release, so it must be adjusted to operate on a minimum battery 

 potential of 44 volts and a minimum trunk insulation resistance of 

 80,000 ohms. The trunk capacity interferes more seriously with 

 the release of the stepping relay than with the release of the line relay. 

 When the ground is removed from the latter the trunk is at zero 

 potential and the charging current through the relay windings is 

 maintained for a very brief period of time but when the incoming end 

 of the trunk is grounded to release the stepping relay in the distant 

 office, the trunk capacity- is fully charged and the discharging current 

 is sustained for a much longer time interval. 



THii Stkppinc Rklav 



The time constant of the line rela\' is such that il cannot be given 

 adjustments which will enable it to meet the more se\-ere require- 

 ments of the stepping relay, and consequently an entirely different 

 t\pe of structure, as shown in F"ig. 17, is used for a stepping relay. 

 This design is of particular interest because it is not used for any 

 other purpose and is the only relay of its type in the telephone plant. 

 Many attempts have been made to replace it with some sort of punched 

 type structure that is more adaptable to the established manufactur- 



